[ui] Fix color picker switcher style for dark-mode
[ui] Fix color picker switcher style for dark-mode

There was a custom dark mode style applied which got inverted by the
dark mode theme which generates inverted colors for the light mode
CSS.

Just removing the custom hover left the inverted-hover color a bit too
dark to see on the dark background.
Fix this by setting the light mode hover grey to one shade darker,
meaning the inverted dark hover is now lighter.

Dark before: https://imgur.com/BmquXSB
Dark after: https://imgur.com/ZaY0lsI

Light before: https://imgur.com/rYgxSsO
Light after: https://imgur.com/uExaLnt

Fixed: chromium:1064959

Change-Id: I44efe8995cb4132725b08e234ec2bb00fc1d4054
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2123480
Commit-Queue: Peter Marshall <6d0eecbeb7fb9d172f49b4b32481d2466fd89429@chromium.org>
Reviewed-by: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend